The crucial role played by the source's degree of spatial coherence in wide-field optical coherence tomography is shown experimentally. Spatially coherent illumination, as obtained with a pulsed laser, generates a considerable amount of coherent optical cross-talk. The latter can be suppressed with spatially incoherent illumination as provided by a thermal or a pseudothermal light source. Demonstration is made for a US air force resolution target covered with a scattering solution made of polystyrene microspheres suspended in water. The origin and nature of cross-talk signals are discussed, as well as specific limitations of spatially incoherent sources.